Pre-heat oven to 350 degrees F.
Combine the dry ingredients. In a medium bowl, add flour, baking powder, baking soda, cocoa powder, and salt. Stir until combined.
In a large bowl or mixer, add butter, brown sugar, and white sugar. Beat at medium-high speed until creamy and fluffy. Add eggs, one at a time, and vanilla. Mix until well incorporated.
Add dry ingredient mixture to egg mixture, ½ cup at a time, mixing slightly between additions. Scrape the side of the bowl and mix until consistent. Don't overmix. (The point of mixing in smaller portions is to keep the flour from puffing into the air.)
Set aside ½ cup each of marshmallows and chocolate chips for after baking. Stir in the rest of chocolate chips and marshmallows.
Using a cookie scoop, drop dough onto an ungreased cookie sheet about 2 inches apart.
Bake cookies in preheated oven for 10-13 minutes. While cookies are in the oven, cut the mini marshmallows in half.
When cookies are finished baking, gently nestle remaining, cut marshmallows into the tops of each cookie and sprinkle with reserved chocolate chips. Perform this step immediately after pulling cookies from oven while they are very hot.